Search

In this experiment 12 rumen-fistulated cows in late lactation, grazing Persian clover (Trifolium resupinatum) at four pasture allowances [9, 16, 32 and 53 kg dry matter (DM)/cow.day], had their entire rumen contents removed and sampled six times over 6 days, with the time of sampling varied between days. These rumen pool size measurements occurred at 0645 hours, 0915 hours, 1045 hours, 1345 hours, 1530 hours and 1900 hours. The cows were offered new allocations of pasture twice daily at 0715 hours and 1530 hours. Herbage intake increased (P < 0.001) from 5.6 to 20.4 kg DM as pasture allowance increased. Pasture allowance had no effects on rumen pool sizes of wet matter (WM) (P = 0.95), DM (P = 0.914), neutral detergent fibre (NDF, P = 0.499) or the DM% of the digesta (P = 0.078). Rumen pool sizes of WM, DM and NDF varied throughout the day. Pool sizes of WM and DM were lowest at 0645 hours and highest at 1900 hours for all allowances (P < 0.001) and along with pool sizes of NDF, were also lower at 0645 hours compared with 0915 hours and at 1530 hours compared with 1900 hours. The lack of increase in rumen pool sizes as pasture allowance increased when cows grazed Persian clover suggests that outflow rates increased with the increasing intakes. The low, and similar, rumination times between allowances also suggests that there is little restriction to the ability of outflow rates to increase when cows graze Persian clover at increasing allowances. The changes in rumen pool sizes over the day were consistent with the twice daily allocation of fresh pasture to the cows. The diurnal rumen pool size information obtained from this experiment will assist with the development of mechanistic rumen models that are capable of simulating the discontinuous intake and varying rumen pool sizes of cows in grazing systems.

Sixteen cows in early lactation were individually fed diets consisting of fresh Persian clover (Trifolium resupinatum)-dominant pasture, offered to all cows at 3.7 kg DM/100 kg liveweight (LW); either alone or supplemented with amounts of crushed wheat ranging from ~0.3 to 0.9 kg DM/100 kg LW (four treatments with four cows per treatment). Cows fed Persian clover alone consumed 19 kg DM/day and total DM intake increased (P < 0.001) in a linear manner as the amount of wheat consumed increased, with no significant effects on clover intake. As the proportion of wheat in the diet increased, dietary neutral detergent fibre (NDF) concentrations declined from 28 to 24%, and in vivo NDF (P = 0.055) and acid detergent fibre (ADF; P = 0.015) digestibilities also declined. There were no significant effects of proportion of wheat in the diet on apparent digestibility of DM, organic matter or gross energy. The extent to which negative associative effects on NDF digestion was associated with the clover could not be determined as it was not possible to distinguish between the NDF derived from clover or wheat, but the decline in ADF digestibility suggested that most of the response lay with the clover since the wheat only contained relatively small amounts of ADF. Ruminal fluid pH was below 6.0 for more than 18 h/day in all cows. There was no effect of wheat in the diet on average ruminal fluid pH, but lowest values during the day were negatively related (P < 0.05) to the proportion of wheat in the diet. As the proportion of wheat in the diet increased, ruminal fluid ammonia-N concentration (P < 0.001) and the acetate + butyrate to propionate ratio (P < 0.001) decreased. The proportion of wheat in the diet did not affect nylon bag estimates of NDF degradation rates for grain or forage. Although most data indicated that effects of proportion of wheat in the diet on the utilisation of consumed nutrients were small, the marginal milk response to additional wheat averaged only 0.9 kg energy-corrected milk/kg DM wheat.

This study investigated the effect of increasing the proportion of forage rape or Persian clover in the diet on dry matter intake (DMI), whole tract digestibility and rumen function. Two experiments were conducted simultaneously; each in a 3 by 3 Latin square design with rumen-fistulated sheep fed either increasing amounts (10, 25 or 40% DM of the diet) of forage rape (experiment 1) or Persian clover (experiment 2). The remaining diet comprised short-rotation ryegrass, cereal-based pellets and maize silage, formulated to give similar metabolisable energy (MJ/kg DM), neutral detergent fibre and protein values between treatments. Purine derivatives excreted in the urine were used to estimate microbial protein synthesis. The study found similar DMI within forage rape and Persian clover treatments, although total DMI was 16% higher for the latter (29 v. 25 g/kg liveweight.day, respectively). The in vivo DM (mean = 0.75) and neutral detergent fibre (mean = 0.65) digestibility coefficients were similar (P > 0.05) within and between experiments. The mean (±s.e.) rumen pH in sheep fed forage rape-based diets (6.17 ± 0.10) was higher than for Persian clover-based diets (5.70 ± 0.09). The efficiency of microbial N supply expressed as microbial N (g/day) per kg of digestible organic matter fermented in the rumen was also similar (P > 0.05) within and between forage rape and Persian clover treatments (mean = 23.4 g microbial N/kg digestible organic matter fermented). The results indicate that increasing the proportion of high nutritive value forage rape or Persian clover within the diet of sheep did not affect the efficiency of feed utilisation.

The objective of this study was to quantify the grazing preference of dairy cows for eight grass, four legume and two herb species in eight seasons over 2 years. All species were grown at the same site, under the same climatic conditions, and with soil moisture and nutrient availability being non-limiting to plant growth. The forage species evaluated were cocksfoot (Dactylis glomerata cv. Kara H0265), perennial ryegrass (Lolium perenne cv. Bronsyn), short rotation ryegrass (Lolium multiflorum cv. Concord), fescue (Festuca arundinacea cv. Advance Maxp.), phalaris (Phalaris tuberose cv. Holdfast), paspalum (Paspalum dilatatum cv. Poir. Common), kikuyu (Pennisetum clandestinum cv. Whittet), prairie grass (Bromus willdenowii cv. Matua), lucerne (Medicago sativa cv. Sceptre), persian clover (Trifolium resupinatum cv. Maral), red clover (Trifolium pretense cv. Astred), white clover (Trifolium repens cv. Kopu II), chicory (Cichorium intybus cv. Grouse) and plantain (Plantago lanceolata cv. Tonic). The 14 forage species treatment plots were laid out in a completely randomised block design with three replicate blocks. The treatment plots were around the circumference of a circle so that the three cows used in each test had unbiased access to all forage species within the blocks. The tests comprised observing the forage being grazed at 10-s intervals for 1 h. The cow preference was recorded as time (min) spent grazing on each forage species. Three Holstein Friesian dairy cows of similar dominance were selected and had grazed all 14 forage species before tests. Cows were fed to requirements before each test so that they would be selective in choice of forages. The most preferred species over the whole year was prairie grass followed by kikuyu and then white clover, despite the fact that kikuyu was not available in winter. Fescue was the least preferred grass species. The mean grazing times for prairie grass and kikuyu during the 1-h test periods of grazing was 11.6 and 10.5 min, respectively. White clover and lucerne were the most preferred legumes (9.6 and 9.0 min, respectively), whereas chicory and plantain were little consumed (3.5 and 3.2 min, respectively). A prediction equation comprising water soluble carbohydrates (WSC%) and nitrate-nitrogen [NO3-N (g/kg DM)] over all seasons and forage species accounted for more variation in cow preference than any other single or combination of variables measured: cow preference [time (min) on plots] = 1.86 + 0.67 WSC% – 1.9 NO3-N (g/kg DM) (r2 = 0.76; s.e. = 2.22; n = 109). The results indicate that the relative palatability of forages can be reasonably well predicted from WSC% and NO3-N concentration, having a positive and negative effect on cow preference, respectively. The prediction equation was improved for groups of species if neutral detergent fibre (NDF%) was included: grasses, cow preference [time (min) on plots] = 24.5 + 0.42 WSC% – 1.31 NO3-N (g/kg DM) – 0.39 NDF% (r2 = 0.87; s.e. = 1.62; n = 57); legumes, cow preference [time (min) on plots] = 3.02 + 0.98 WSC% – 2.15 NO3-N (g/kg DM) – 0.08 NDF% (r2 = 0.92; s.e. = 1.38; n = 36); and herbs, cow preference [time (min) on plots] = 19.41 + 0.22 WSC% – 1.74 NO3-N (g/kg DM) – 0.69 NDF% (r2 = 0.53; s.e. = 1.81; n = 19).